Cementing plug



Aug. 1, 1939.

s'. R. ROBINSON 2, 67,778

CEMENTING PLUG Filed April 6, 193a it'll hill Patented Aug. 1, 1939UNITED STATES PATENT OFFICE GEMENTING PLUG Calif.

Application April 6, 1938,, Serial No. 200,400

2 lJlaims. (Cl. 166-1) This invention relates generally to oil wellcementing operations and particularly to plugs used in such operations.

In the drilling of oil wells water sands are often encountered above theoil sands, the two sands usually being separated by a relativelyimpervious strata of rock or shale which prevents the water fromentering the oil sands. The water, between its confining strata, may beunder considerable pressure so that as the drilling of an oil wellprogresses and the drilling tools perforate the confining strata aboveand below the water bearing sands the water flows into the well. Ifdrilling is continued into the oil sands without shutting off the waterthe water will follow the bore hole into the oil sands and the water andoil will become mixed together. It is therefore necessary to seal offthe water by some means.

The ordinary method of sealing off the water is to set casing at a pointbelow the water sands, cementing the casing to the formation. This isaccomplished by withdrawing the drill string from the hole and loweringthe easing into the hole. Ordinarily before the casing is lowered intothe hole a float shoe having a check valve therein which allows downwardpassage of fluid therethrough, is mounted on the lower end of thecasing. Vertically spaced above the float shoe a suitable distance ismounted a float collar which is also provided with a similar checltvalve. The casing is lowered into the well until it rests on the bottomof the hole, after which it is raised a short distance so that thebottom of the casing will be spaced above the bottom of the hole.Circulation is then established by pumping fluid down the casing, thefluid emerging at the bottom of the casing and flowing up the hole onthe outside of the casing.

After the circulation has been established, a cementing plug, known as abottom plug, is placed in the casing at the top. This plug is adapted toyieldingly engage the sides of the casing. The desired amount of cementslurry, according to the requirements of the particular job beingperformed, is then pumped into the casing on top of this bottom plug.After this operation a top plug is placed in the casing and fluid isforced into the casing on top of the top plug forcing both cementingplugs and the cement confined between them downwardly to the bottom ofthe casing until the bottom plug strikes against the upper face of thefloat collar. I

Continued pumping of fluid into the top of the casing forces the cementaround the bottom plug and through the float collar and float shoe intothe formation around the lower end of the casing. As pumping continues,the top plug strikes the lower plug and as the topplug is not designedto permit passage of fluid, the pressure in the casing immediatelyincreases, indicating that the cement has been forced from between theplugs.

Following this operation the cement is allowed to set. After the cementhas set drilling may again proceed, the cement in the casing, the plugs,and the float collar and float shoe being drilled out.

The ordinary bottom plug used in cementing operations comprises a memberhaving an enlarged head substantially the size of the internal diameterof the casing and through which passages are formed for the flow orby-passing of cement therethrough. The top of the bottom plug isprovided with a flexible member or wiper for engaging the inside of thecasing. It is essential to a successful cementing operation that thisplug be dropped into the casing with the top end uppermost. If it isplaced in the casing upside down the flexible casing engaging memherwill seat on the float shoe and effect a sealing or plugging of thepassage through that member. It frequently happens that through thecarelessness of a workman the bottom plug is placed in the casing upsidedown with the result that the passage in the float collar is bloclredand the cement is retained in the casing above the bottom plug. lit thenbecomes necessary to drill this column or cement out, pull the casing,insert a new float collar and shoe, lower the casing and perform thecementing operation again.

it is also true that whenever a cementing operation goes wrong or isunsuccessful the excuse is made that the bottom plug was put in upsidedown, and as this is a point about which no one can be certain after theplug has reached the bottom of the hole, the operators are often misledas to the real cause of failure of the cementing operation.

It therefore is a primary object of this invention to provide a bottomplug for use in oil well cementing operations which is fool proof andwhich will function properly no matter which end of the plug is placeduppermost. In this connection it is an object of this invention toprovide a plug which primarily consists of a member having a flexiblecasing engaging member, termed a wiper, intermediate its length, bothends of the plug having passages therein or therethrough so that nomatter how the plug is inserted in the casing circulation may bemaintained through the casing past the plug when the plug rests upon thefloat collar.

These and other objects will be apparent from the drawing and thefollowing description thereof. Referring to the drawing, which is forillustrative purposes only,

Fig. l is a fragmentary sectional elevation of a bore hole showing thecementing plug of this invention in operative relation with the casingand other elements used in a cementing operation.

Fig. 2 is an enlarged sectional elevation of the plug shown in Fig. 1.

Fig. 3 is a top plan view of the plug of Fig. 2.

Fig. 4 is an elevation, partly in section, of another form of plug.

More particularly describing the invention, reference numeral I!generally indicates the lower portion of a bore hole which is showntraversing a stratum l2, a stratum l3 of water fllled sand formation, arelatively impervious stratum l4, and partially penetrating an oil sandstratum IS.

A casing, generally indicated by reference numeral I6 is shown in thebore hole and partially raised oif the bottom of the hole. The lower endof the casing is provided with a float shoe H which has a passageway i8therethrough controlled by a check valve l9 which is adapted to permitdownward passage of fluid through the passageway l8 but to preventupward passage of fluid therethrough. Spaced above the float shoe is afloat collar 20 which is also provided with a passageway therethroughindicated by reference numeral 2| which is controlled by a check valve22 similar in all respects to the check valve I9 above described.

The float collar and float shoe are ordinarily constructed of a readilydrillable material except for the portion which forms a continuation ofthe casing wall. Thus, the valve seat and cage are often of Bakelite setin a body of cement.

Shown above the float collar 20 and resting on the upper end thereof isthe bottom cement plug of this invention, generally indicated byreference numeral 24. Above this plug is a body of cement slurry 23which has been placed in the casing on top of the plug. On top of thiscement slurry is the top cementing plug 26 which separates the cementslurry from the fluid pumped into the well and prevents mixing of thosetwo liquids.

The casing 18 has been shown raised ofl the bottom of the hole in aposition where circulation may be established downwardly through theinterior of the casing outwardly through the float shoe l1 and upwardlyexteriorly of the casing. In the cementing operation, after circulationhas been established the plug 24 is placed in the top of the casing andcement slurry 25 pumped in on top of it until the desired amount hasbeen placed in the casing. The plug 23 is then placed on top of theslurry and liquid is pumped on top of plug 26, forcing the two plugsdownwardly in spaced relation with the. body of cement slurry 25conflned between them. The drawing (Fig. 1) illustrates the position ofthe plugs at the time the bottom plug comes to rest upon the floatcollar. Subsequent pumping of liquid into the top upwardly in the holesurrounding the casing and to some extent enter the formation.

Referring to Figures 2 and 3 for details in the construction of thebottom cementing plug of this invention, the plug essentially comprisesa member having enlarged fluted end portions and an annular flexiblewiper encircling a reduced middle portion and extending beyond the outerdiameter of the other portions of the plug.

More particularly the plug comprises a cylindrical central body portion28 upon which is formed on each end segmental end portions 29 havingcurved outer surfaces 3i],v which together form an interruptedcylindrical surface. These segmental end portions extend beyond the endof the portion 28 and form a cup-like recess 3| at each end of the plug.The end surfaces 32 of the portions 29 are flat.

Separating the segmental portions 29 at each end of the plug are fourradially disposed passageways, grooves, or flutes 33 which act as fluidpassageways for the purpose of permitting fluid to by-pass the ends ofthe plug.

The inner ends of the segmental end portions 29 are inwardly tapered at34 to provide a reduced middle portion on the plug. Surrounding themiddle of the plug is an annular flexible casing engaging member 35which will be termed a wiper. The entire plug of Figures 1 to 3 ispreferably made of rubber, although other suitable substances may beemployed.

The plug has been shown as comprising a body portion upon which ismounted a flexible wiper. The wiper may either be formed of a materialflexible enough to permit mounting of it by expanding it over the endsof the plug or it may be split and vulcanized into place. It is alsopossible to form the plug and wiper in one piece. It is furthercontemplated to be within the scope of this invention to form the bodyof the plug in two pieces adapted to be threaded together after thewiper is placed between them.

When in use the plug may be inserted in the casing with either enduppermost and it will serve to retain the cement slurry 25 above it asthe cement is placed in the casing and forced downwardly therein aspreviously described. When the plug comes to rest on the top of thefloat collar further pressure upon the column of material in the casingabove the plug causes the cement slurry to by-pass the plug 24. In-by-passing the plug the cement passes through the grooves 33, deflectsthe member 35 and passes between that member and the casing anddownwardly through the grooves 33' in the lower end of the plug into thecup portion 3| from which it escapes into and through float collar 20.

It should be readily apparent that with this construction the plug maybe inserted in the casing with either end uppermost and will functionequally well in either position.

Although the plug has been shown and described as having radiallydisposed grooves at each end to form the fluid passages, it iscontemplated to be within the scope of this inven tion to provide someother form of passageway through the enlarged end portions of the plug.Inthis connection a central bore at each end of the plug terminating inone or more outlets in the region of the reduced portion of'the plugmight be used, as described in connection with the other form of theinvention shown in Fig. 4.

In Fig. 4 there is shown a plug constructed of wood'except for the wiperportion. This plug comprises an end member 38 and an end member 39. Eachof these members is provided with a threaded dowel indicated byreference numerals and 4| positioned in recesses 42 and 43 of therespective members 38 and 39. The dowels are secured in place by meansof pins 44 and 45 respectively.

In this form of the invention it is contemplated that the members 38 and39 be made of a relatively soft wood such as redwood and therefore thedowel members 40 and 4| are made of a harder wood, as it is difficult toproperly thread redwood. An intermediate member 46 is providedofrelatively hard wood which has a central threaded bore 41 adapted toreceive the dowels 40 and 4| to secure the parts together. Interposedbetween the members 38 and 46 is the annular flexible member or wiper48, which may be formed of rubber.

Each of the members 38 and with enlarged end portions 38' and 39respectively. These end portions have a central passageway therethroughwhich terminates in a pair of lateral openings 5| which have their outerend portions on a concave surface 52.

The operation of this plug is the same as the other form of plug. Whenthe plug comes to rest on the float collar the concrete slurry bypassesthe plug through the passages 50, 5| at the ends of the plug and passesbetween the easing and the reduced middle portion of the plug past theflexible wiper 48 which is deflected by the pressure of the fluid.

Although the plug has been shown as comprising three main members, it iswithin the scope 39 are provided of this invention to form the bodyportion of the plug in two members instead of three, and thread one ofthese members into the other, such construction necessitating the use ofa harder wood. It is also contemplated that some material other thanwood might be utilized in the construction of the plug.

I claim as my invention:

1. A cementing plug of the type described comprising two end members,said end members each having an enlarged outer end portion and having apassageway therethrough establishing communication to both sides of theenlarged portion, an intermediate member between said end members, meansfor detachably securing said members together, and an annular flexiblewiper mounted between one of said end members and said intermediatemember, I

2. A cementing plug of the type described comprising two end members ofrelatively soft wood, said end members each having an enlarged outer endportion and having a passageway therethrough establishing communicationto both sides of the enlarged portion, an intermediate member ofrelatively hard wood between said end members. said intermediate memberbeing provided with a threaded bore, a threaded dowel of relatively hardwood secured in the inner end of each of said end members and threadedinto the threaded bore of said intermediate member, andv an annularflexible wiper mounted between one 01' said end members and saidintermediate member.

, SLAYDEN R. ROBINSON.

